This invention relates to nuclear magnetic resonance (NMR) methods. More specifically, this invention relates to a method for minimizing or eliminating artifacts induced by breathing method of a patient undergoing an NMR examination using Fourier transform (FT) NMR techniques.
Acquisition of diagnostically useful images of the upper torso and abdomen utilizing FT NMR techniques is often complicated by motion-induced artifacts, which arise from respiratory movement of thoracic or abdominal regions of a subject during the data acquisition period, which can be quite long. The primary cause of motion is patient breathing. The source of these artifacts has been determined to be motion-induced phase and amplitude errors in the phase-encoding direction when using FT imaging techniques, such as the one commonly referred to as "spin warp". It has been found that the greatest contribution to the artifacts is simple geometric motion, as opposed to movement-induced diamagnetic or paramagnetic field changes, or detuning effects on the radio frequency (RF) coil system.
Numerous approaches have been suggested for minimization of these artifacts. Among the approaches suggested are breath holding, various gating schemes which involve data acquisition during expiration/inspiration, and controlled shallow breathing. However, all of these techniques involve either patient cooperation or increased scan time based on the full breathing cycle. Specific drawbacks associated with the proposed conventional techniques are, for example, that respiratory gating requires additional equipment to generate the gating signals and generally prolongs the actual imaging time. Breath holding and shallow breathing may work well with the volunteers but are difficult or impossible for seriously ill or incapacitated patients who are the most likely subjects for NMR imaging.
It is therefore a principal object of the invention to provide a method of scanning subjects which reduces or eliminates motion-induced artifacts.